Swash plate axial piston compressors for generating compressed air for a variety of devices in motor vehicles are generally known. These compressors typically include a drive shaft, a cylinder block surrounding the drive shaft, which cylinder block has cylinder bores formed therein, and a plurality of pistons slidably disposed in the cylinder bores, wherein the pistons are successively reciprocated in the cylinder bores by a rotation of the drive shaft so that a suction stroke and a discharge stroke are alternately executed in each of the cylinder bores. One such device is disclosed in U.S. Pat. No. 5,626,463 to Kimura, which describes a cam plate member that rotates with a drive shaft, and a non-rotating wobble plate mounted on the cam plate that pivots in accordance with the rotating cam plate member, thereby axially displacing the pistons inside the bores.
One disadvantage of these compressors, however, is that the swash plate assemblies are complex and require a large number of parts. Additionally, compressors of this type require a relatively large space. Accordingly, in order to reduce the complexity of the design and reduce the number of parts used and space required, it has been proposed to use a swash plate air compressor employing pistons disposed in bores of a stationary cylinder block, wherein a non-rotatable swash plate pivots in accordance with the thrust exerted by an actuator, such as that disclosed in U.S. Pat. No. 6,439,857, which is assigned to the assignee of the present application and which is incorporated herein by reference.
However, in order to keep the swash plate from rotating along with the drive shaft, it is necessary to provide a mechanism that simultaneously permits the swash plate to pivot as described above, yet restrains the swash plate from moving rotationally. These mechanisms typically employ a ball or stopper, such as that disclosed in U.S. Pat. No. 6,439,857, that slides along a track or groove in the compressor housing.
These arrangements, however, have the disadvantage that they are not able to work effectively in an oil-free operation of the compressor, which is desired in order to prevent oil contamination of, for example, an airbrake system for which the compressor generates compressed air. Without the presence of oil to keep the surfaces lubricated, the continuous sliding of surfaces used to prevent the swash plate from rotating creates undesired friction that wears down these surfaces and impractically limits the life of the compressor.
Another disadvantage of these arrangements is that they cause the pistons to move erratically within the cylinder block, which creates several undesired effects. First, this will often lead to excessive wear of the pistons and the walls of the cylinder block. Second, it will require a greater piston to head clearance than would be required if the pistons moved smoothly within the cylinder block, which decreases the volumetric efficiency of the compressor.
What is desired, therefore, is an apparatus for restraining a swash plate from rotating with a drive shaft that permits oil-free operation of the compressor. What is further desired is an apparatus for restraining a swash plate from rotating with a drive shaft that increases the life of the containment device, the housing walls, the pistons, and the walls of the cylinder block. What is also desired is an apparatus for restraining a swash plate from rotating with a drive shaft that increases the volumetric efficiency of the compressor.